Big Sur is designed to frustrate me – I’m convinced of it!

I took a screenshot of multiple apps to compare and contrast. This is a window sidebar, and theoretically should work and look pretty identical. Instead… that is not the case.

Left to right in the screenshot, we have: Mail, Notes, Calendar, Music, Finder, and Reminders. (Reminders is the current window, thus the slight variation in contrast. The lack of contrast in Big Sur remains a disgrace.)

Here is what I notice.

Numbers are treated differently. Sometimes numbers indicating items are in a little bubble, sometimes just text. Sometimes they’re aligned. Sometimes not.
Some groups can collapse, some can't. “Library” in Music looks like a collapsable group, but it isn’t. An “Edit” option appears on hover… but despite looking the same as other groups, it isn't.
Search is sometimes here, sometimes not. In thinking about it more, the sidebar is the best spot for a search field – having it in the upper right of a window (which happens in a number of apps) breaks the relationship between the search scope and the physical area of the app it is in.
Window buttons aren't in the same spot. Incredibly, Calendar fucks this up.
Controls in this sidebar are okay sometimes. Calendar, again, fucks this up. Buttons! In the old toolbar! And they only apply to the top area here. Notes adds “New Folder” to the bottom left just because, and Reminders add “New List”. Reminders also has those totally-off big buttons here instead of a damn list. WTH?
Notes uses its own font for REASONS. They’re bad ones.
Font sizes are different. Reminders and Calendar are smaller.
Only Mail has groups within items. Look at “All Drafts”. I can expand that out. Can’t do that in Notes, which has nested items. Why not?
All headers for collapsed groups are actionable and don't look that way. Every single header here in every app has some action associated with it, but they only show up on hover – and outside of the aforementioned “Library” in Music, they’re expand/collapse.

Let’s face it: Big Sur is a UI shitshow. It certainly looks like Apple put usability and consistency on the back burner.